1. Field of the Invention
The present invention relates to a tearable membrane switch, particularly, a membrane switch for use with an air bag mounted in the steering wheel of a vehicle.
2. Description of the Related Art
A membrane switch for a vehicle has usually a pair of contacts made of copper. Therefore, the surfaces of the contacts are apt to be covered by oxide film or hydroxide film, thereby gradually increasing the contact resistance of the membrane switch. Generally, such a contact is formed from a copper film bonded to a base film sheet, and it may become thick and stiff. A membrane switch employing such contacts may not be suitable for a horn switch for a vehicle which is equipped with an air bag system because the horn switch that is installed in the steering wheel must tear when an air bag accommodated in the steering wheel is inflated. However, the above contacts may be too stiff to tear for the air bag to be inflated in a short time.
If the material of the contacts is changed to mixture of silver powder and carbon powder, the contact resistance necessarily increases to a level not suitable for the horn switch.